If you stored dahlia tubers over the winter, by now you have removed them from storage and checked their viability. Each tuber must have an eye or it will not grow. Most dahlia suppliers have stopped sales on-line by now, so if you haven’t purchased varieties you want for this season, local dahlia societies (CT, PTown and RI) will be selling tubers this month or next.

Tubers in hand, you can start your plants inside using a good potting mix. (I like general purpose ProMix with mycorrhizae.) Many varieties will poke through the surface after a week or two. Once the plants have sprouted, water them regularly. They should be grown under lights kept four to six inches above the plants to keep them from becoming spindly.

The next step is to prepare your garden. If you are growing dahlias for the first time, you will need to select a site for your dahlia bed. Dahlias need six to seven hours of direct sunlight daily for optimum growth but will do reasonably well with four hours of sunlight a day (although they will bloom later). The richer the soil is in organic material, the better the blooms will be from your plants. Make sure the area you select drains well. Dahlias require a lot of water while growing but the tubers do not like to sit in water. So, good drainage is essential. A soil test at this time would be valuable if you haven’t done one for a while. Soil that is too acidic or too alkaline will hinder the plant’s ability to absorb the nutrients it needs. Soil pH between 6.5 and 7 ensures that your dahlias will efficiently absorb the necessary nutrients from the soil.

— Donna Lane (NEDS president)

Memorial Day weekend is typically the time to plant dahlias. Ground temperatures should be about 60 degrees F. Dahlias will struggle in cold soil.

If you are planting tubers, make sure your soil is not too wet. Plant the tuber 4 to 6 inches deep, with the tuber flat and eye pointing up, and place a tall stake in back of the tuber (see diagram). Cover the tuber to the soil line. Unless your soil is very dry or spring weather is extremely warm, do not water at planting time. More tubers are lost due to rot in wet, cold soils than from any other cause. Water well when foliage begins to emerge, then keep well watered.

Suggested spacing is 2-feet between plants, 3-feet between rows. Plants should have good air circulation in order to prevent fungal problems.

Light weeding and cultivation between rows at planting time is OK, but take care. When the plants are about a foot tall, they will have been making feeder roots. These roots are fairly close to the surface, so limit further cultivation.  

If you started the tubers inside, make sure you have hardened off the plants before putting them in the ground.  Many growers remove one or two sets of lower leaves and set the plants a bit deeper than they were growing in the pot. After planting, water with a transplant solution. Plants must be kept well watered from this point on.

Keep your eye out for insect pests. The most common are slugs, earwigs, spider mites, potato leaf hoppers and caterpillars. Wireworms can sometimes be problematic as well. If you don’t know what is eating your plants, inspect your garden at night with a good, strong flashlight.

And watch for signs of 4-legged pests, most notably woodchucks. They have been known to devour dozens of tender leafy plants in a single sitting.

Keep your eye out for virused plants as well. For more information on virus in dahlias, go to http://dahlia.wsu.edu

— Donna Lane (NEDS president)

Tie

As dahlias grow, they need to be supported to promote straight stems and to prevent damage from heavy winds and rain. Tie your dahlia stalks to the stake you pounded in at planting time. Start tying when the plant is 12 to 18 inches tall, and continue tying every 12 to 18 inches up to about 4 feet. Don’t tie the stalk so tight that it will pinch or damage it. 

Stop/Top

Stopping/Topping is the method used to force dahlia plants to produce multiple branches and, therefore, more blooms. To stop your plant, pinch off the growing tip of the plant. The number of leaf pairs to save depends on the size of the bloom. For plants with giant or large blooms, two or three leaf pairs should remain; with medium or small blooms, three or four leaf pairs should remain. For smaller varieties, stop once the terminal bud has formed.

Disbranch

Disbranching is the removal of some of the laterals (or branches) to concentrate all of the growing energy into the remaining blooms in order to maximize their size.

Disbranching is done several weeks after stopping a plant. See diagram below.

— Donna Lane (NEDS president)

Water, Water, Water

The heat of summer dries out the soil very quickly, so it’s important to have a regular watering schedule. Drip irrigation is the most effective means of delivering water directly to your dahlias without wetting the foliage, but soaker hoses are also a good means of getting the water to the roots where it’s needed. Overhead watering is not as efficient and may damage the flowers. Deep, less frequent watering is more effective than small doses of water. Water early in the day and soak the plants two or three times a week.

Scout for Pests, Fungus and Virus

A daily walk-through of the dahlia garden will help you prevent major insect, disease or viral outbreaks. Things to watch out for:

VIRUS: stunted plants; misshapen leaves; interveinal yellowing

INSECTS: Japanese beetles; aphids; earwigs; potato leafhopper; grasshoppers; spider mites

FUNGUS: powdery mildew (it won’t kill the plant, but its spread inhibits photosynthesis). Prevention is the best defense. If you foliar feed your dahlias, you may want to add a fungicide to your fertilizer mixture.

Continue Disbudding Your Plants

Disbudding allows the terminal bloom to reach its maximum size. The easiest method to remove buds is to get to them when they are small (about the size of a pea) and just pinch them out with your fingers. The best time to disbud is morning when the plants are most turgid. Do not disbud more than the first pair of buds on the smaller types of dahlias (e.g., pompons).  For larger blooms, it may be necessary to also remove some of the lower buds. See illustration below.

— Donna Lane, NEDS president

Review the July growing guide. Continue watering and scouting for pests, fungus and virus. Make sure to deadhead your plants and to pick and enjoy your blooms.

Early morning is the best time of day to cut flowers. The plants are most turgid at that time of day, which reduces wilting. Carry a container of water so the stems can be immersed immediately after cutting. Adding a commercial flower preservative also helps keep the flowers fresh.

To condition your blooms, place them in a cool, dark place for four to eight hours. They will last a lot longer in the vase or arrangement if you do this.

— Donna Lane, NEDS president

Dahlias are their most beautiful in September! The warm days and cool nights are what these plants thrive on! Some areas of New England may have a killing frost in September, but most will not. (If you do, see the October write-up for digging and preparing tubers for winter storage.)

Your dahlia tubers will need to harden for the winter, so discontinue all fertilization and start limiting the amount of water you provide to your plants.

This month is a great time to visit local dahlia shows (see listing of 2016 shows), commercial dahlia farms, and other dahlia gardens to note varieties that you might like to add to your collection next year.

If you are interested in trying to propagate new varieties from seed next year, you will want to collect seed this month.

— Donna Lane, NEDS president

Coming soon. . .

Coming soon. . .